Starch, modified starch and starch/plasticizer composites have sometimes been used in various compositions which might have included elastomer formulations, for various purposes which might have included tire components such as tire treads.
Such materials might be used alone or in conjunction with silica and/or carbon black reinforcing fillers or also with other fillers such as, for example, recycled, or ground, vulcanized rubber particles, short fibers, kaolin clay, mica, talc, titanium oxide and limestone. Such short fibers can be, for example, fibers of cellulose, aramid, nylon, polyester and carbon composition.
U.S. Pat. Nos. 5,403,923, 5,258,430, and 4,900,361 disclose the preparation and use of various starch compositions and U.S. Pat. No. 5,672,639 relates to use of starch/plasticizer composites in rubber compositions including as a tire component such as a tire tread.
However, use of starch-based fillers, in general, may present some limitations as reinforcement for various elastomers where resistance to abrasion and tear properties for elastomer composition are significantly desirable properties.
Accordingly, it is desired to enhance the use of starch-based materials in elastomer compositions.
Historically, starch may typically be represented as a carbohydrate polymer having repeating units of amylose (anhydroglucopyranose units joined by glucosidic bonds) and amylopectin, a branched chain structure, as is well known to those having skill in such art. Often, starch is composed of about 25 percent amylose and about 75 percent amylopectin. [The Condensed Chemical Dictionary, Ninth Edition (1977, revised by G. G. Hawley, published by Van Nostrand Reinhold Company, page 813]. Starch can be, reportedly, a reserve polysaccharide in plants such as, for example, corn, potatoes, rice and wheat as typical commercial sources.
Starch by itself typically has a softening point of about 200.degree. C. or above and, therefore, usually is thought of as having a somewhat limited use in many rubber products, primarily because rubber compositions are normally processed by preliminarily blending rubber with various ingredients at temperatures in a range of about 140.degree. C. to about 170.degree. C., usually at least about 160.degree. C., and sometimes up to 180.degree. C. which is not a high enough temperature to cause the starch (with softening temperature of at least about 200.degree. C.) to effectively melt and efficiently blend with the rubber composition. As a result, the starch particles tend to remain in individual domains, or granules, within the rubber composition rather than as a more homogeneous blend.
Accordingly, starch is sometimes modified with a plasticizer of lower softening point to create a starch/plasticizer composite for use in rubber compositions.
The term "phr" as used herein, and according to conventional practice, refers to "parts of a respective material per 100 parts by weight of rubber, or elastomer".
In the description of this invention, the terms "rubber" and "elastomer" where used herein, may be used interchangeably, unless otherwise prescribed. The terms "rubber composition", "compounded rubber" and "rubber compound", where used herein, are used interchangeably to refer to "rubber which has been blended or mixed with various ingredients and materials" and such terms are well known to those having skill in the rubber mixing or rubber compounding art.
The term "carbon black" as used herein means "carbon blacks having properties typically used in the reinforcement of elastomers, particularly sulfur curable elastomers".
The term "silica" as used herein can relate to precipitated or fumed silica and typically relates to precipitated silica, including an aluminosilicate, which is well known to those having skill in such art.
A reference to an elastomer's Tg refers to its glass transition temperature, which can conveniently be determined by a differential scanning calorimeter at a heating rate of 10.degree. C. per minute.